Consequences of Neutron Energy Spectrum on Radiation Damage, Gas Production, and Transmutations in Fusion Materials

The inclusion of test modules in the U.S. Fusion Prototypic Neutron Source (FPNS) offers the opportunity to test a wide variety of materials in a representative radiation environment of the fusion Pilot Plant, DEMO, and power plant. The testing may include various generations of structural materials for conventional and advanced blanket and divertor concepts. Since all structural materials derived from the fission industry are inadequate for fusion applications (due to the more damaging effects of the 14-MeV fusion neutrons), radiation-resistant reduced-activation structural materials (reduced-activation ferritic-martensitic steel, vanadium alloy, W alloy, and SiC/SiC composites) were specifically developed for fusion and could be tested in the FPNS to qualify for the highly irradiated fusion components surrounding the plasma. The large atomic displacement and the helium and hydrogen generations by fusion neutrons are unique to fusion materials. The most important attribute for the FPNS would be the typical fusion-relevant He/displacements per atom (dpa) ratio of ~10 for steel in particular. By comparison, irradiation in the fission spectrum of the High Flux Irradiation Facility (HFIR) would underestimate the dpa and provide a very low He/dpa ratio of ~0.3 for steel, which is irrelevant to fusion. This paper reviews the neutron irradiation impacts and presents a few examples of dpa and transmutation products for steel, W, and SiC based on modeling in several fusion design studies. The operating conditions of advanced U.S. fusion power plants were considered along with the credible lifetime goal of 200 dpa and 20 MW·yr/m² fluence that could be achieved with directed research and development programs coupled with the construction of the FPNS 14-MeV neutron facility.